1. Field of Invention
This invention pertains to the hydrogenolysis of alditols such as sorbitol to produce glycerol and glycol products using an improved continuous fixed bed catalytic process.
2. Description of Prior Art
The production of glycerol and polyols by hydrogenolysis of sorbitol has been widely studied. Generally, an optimum 30-40 W % of glycerol congeners has been reported in the product obtained from autoclave batch reaction processes. The reaction conditions used are high hydrogen partial pressure of 2000-5000 psig, temperature of 200.degree.-250.degree. C., (392.degree.-482.degree. F.), long residence time of 1.5 hours or more, and use of fine nickel powder catalyst of 100-200 mesh size in the form of a slurry with the feed.
A disclosure regarding hydrogenolysis of sorbitol is provided by Clark in Industrial & Engineering Chemistry, Vol. 50, No. 8 (Aug. 1958), pages 1125-1126. Aqueous solutions containing 40% of 99% D-sorbitol were used with 1% calcium hydroxide promotor and 50% nickel on kieselguhr catalyst suspended in a slurry with the feed in a stirred reactor. Conditions used were 2000-5600 psi hydrogen partial pressure, 215.degree.-245.degree. C. (419.degree.-473.degree. F.) temperature and reaction times up to 400 minutes (6.7 hrs) to produce glycerol, ethylene glycol, propylene glycol, and other more minor products.
U.S. Pat. No. 2,965,679 to Conradin discloses a similar process for producing glycerol and glycols from sugar alcohols using a suspended nickel on kieselguhr catalyst in an autoclave type reactor. Reaction conditions are 200.degree.-300.degree. C. temperature, 500-1000 atmospheres pressure and pH of 8-10, followed by filtration to remove catalyst and separation of the products.
Van Ling et al disclosed in Journal of Applied Chemistry, Vol. 19, 1969, pages 43-45, hydrogenation experiments using slurried catalyst in autoclave reactor on feeds of sucrose, glucose and fructose in methanol-water solution to produce glycerol. Catalyst used was CuO-CeO.sub.2 -SiO.sub.2 with 0-5% Ca(OH).sub.2 addition to feed. Reaction conditions used were 200.degree.-250.degree. C. temperature, 100-300 atmospheres pressure and 10-120 minutes reaction time. Van Ling et al further disclosed in Industrial and Engineering Chemistry, Vol. 9, No. 2, 1970, pages 210-212, a process for hydrogenolysis of sucrose to make glycerol, using two stirred reactors connected in series. The sucrose was mixed with methanol-water solvent and CuO-CeO.sub.2 -SiO.sub.2 catalyst and reacted at 200.degree.-225.degree. C. and 200 atmospheres pressure, after which glycerol can be recovered by multi-stage distillation.
U.S. Pat. No. 3,341,609 to Kasehagen discloses a process for producing glycerol and glycols using Raney nickel catalyst in slurry form at 190.degree.-220.degree. C. and pressures up to about 2000 psig, followed by separation and distillation steps. U.S. Pat. No. 3,471,580 to Hellwig et al discloses that by using a single or multi-stage upflow ebullated bed catalytic reactor at 200.degree.-550.degree. F. temperature and 700-3500 psia hydrogen partial pressure, glycerol and glycols can be produced from saccharides. Examples of the conditions used for converting a sorbitol type feed to glycerol in a single stage reaction were about 375.degree. F. temperature, 1700 psia hydrogen partial pressure, 1.2 liquid hourly space velocity (LHSV), and using nickel on alumina catalyst to produce roughly 50 W % glycerol and 20 W % propylene glycol, with the remainder being methanol, ethanol, isopropanol, and other products.
It is believed that none of these known processes are presently being used commercially to produce glycerol and related products on a continuous basis. Thus, further process improvements in alditol conversion are needed for achieving continuous operations at reduced reaction conditions and increased glycerol product yields are desired, particularly using improved catalysts in fixed bed reactors. By selecting optimum catalyst size, some increase in catalyst age can be achieved before regeneration is needed.